1. Field of the Invention
The present invention relates to a video signal processing device for synthesizing a plurality of interlace video signals which are asynchronous to each other and generating output video signals, and a method of the same, and relates to a vehicle-mounted camera system applying the video signal processing device, which is a system mounted on a vehicle and the like, for imaging areas around the vehicle in different directions with a plurality of cameras and displaying the images for the driver thereof.
2. Description of Related Art
A vehicle-mounted camera system for image display is a driving support system for presenting a driver with an additional visual information in cases where a vehicle is moving backward and forward, such as when parking a vehicle in a garage and when pulling over to the kerb, or where a vehicle is moving into an intersection or a T intersection with poor visibility. In this system, images of the area to the rear, the area to the left front, and the area to the right front of the vehicle are imaged by a plurality of cameras connected to a camera controller, and displayed to the driver as rear and blind corner views.
In such a vehicle-mounted camera system for image display, it is necessary to lay out the plurality of the imaged images on one screen or to join the images together by the camera controller, so as to simultaneously display, for the driver, the plurality of images of the areas around the vehicle imaged in different directions by the cameras.
As a technique for synchronizing images imaged by a plurality of cameras, Japanese Patent Application Publication Laid-open No. 1999-317908 discloses a camera system in which a camera controller of a plurality of cameras creates a synchronizing signal and transmits it to the cameras, and each camera transmits a video signal in accordance with the synchronizing signal to the camera controller. Since the video signals are transmitted from the plurality of cameras to the camera controller in accordance with the same synchronizing signals, it is prevented the occurrence of image distortion when switching. By performing conversion processing on a plurality of video signals and the like using the same method, video signals for one screen can be generated by the camera controller of the vehicle-mounted camera system for image display.
However, the above-mentioned system requires a unit for generating a synchronizing signal in the camera controller, and also requires providing a signal line for supplying the synchronizing signal to each camera. Thus, there arises a problem of the complication in configuration of a device.
There is a technique for the synchronization of video signals imaged by a plurality of cameras without using a synchronizing signal, in which video signals from each camera are temporarily stored in a buffer in a camera controller.
In this method, a camera controller for receiving video signals from a plurality of cameras is provided with three planes (storage sections) of input buffers, each of which has a memory capacity equivalent to one frame (for example, equivalent to 640×480 pixels if a video signal is for the VGA system), for each of cameras connected. The camera controller sets: any one of the three planes as an input plane for storing video signals transmitted from the camera; another plane as a waiting plane having video signals temporarily stored for synchronization; the other one as an output plane outputting video signals for performing image conversion processing. Then, the function of each plane is caused to sequentially rotate.
Since the cameras transmit video signals to the camera controller at timings in accordance with respective internal clocks therein, the start timings of frame durations of the video signals transmitted from the plurality of these cameras go out of synchronization, and the way of going out of synchronization becomes non-reproductive.
If a video signal for one frame is inputted from the camera to the input plane in each input buffer for each camera, the camera controller sets the input plane as the waiting plane. Then, at the time when video signals each for one frame are inputted into the input buffers corresponding to all cameras, the waiting planes of the input buffers corresponding to all cameras are set as the output planes.
Thereafter, the camera controller simultaneously reads out video signals stored in the output planes of each input buffer. In other words, the plurality of video signals inputted from the respective cameras are simultaneously readout. Then, the camera controller performs the image conversion processing for displaying the image on a monitor or the like. A CPU in the camera controller reads out the video signals to be stored in the output planes of the input buffers frame by frame, in accordance with input buffer readout addresses stored in pattern memories. Subsequently, after performing address conversion processing, video signals for monitor display are created, which are stored in an output buffer.
Note that size of an address space provided in the pattern memory storing the addresses for the conversion processing equals the resolution of the monitor which presents a driver with an image after the address conversion (for example, VGA (640×480 pixels) size).
Hence, it is possible to absorb the a synchronization of the video signals inputted from the plurality of cameras, thus making them synchronous.